Chapter 15, Problem 71E

Potassium hydrogen phthalate, known as KHP (molar mass = 204.22 g/mol), can be obtained in high purity and is used to determine the concentration of solutions of strong bases by the reaction

${\text{HP}}^{-}(aq)+{\text{OH}}^{-}(aq)\to {\text{H}}_2\text{O}(l)+{\text{P}}^{2-}(aq)$

If a typical titration experiment begins with approximately 0.5 g KHP and has a final volume of about 100 mL, what is an appropriate indicator to use? The pK_a for HP⁻ is 5.51.